cc: Do not create separate tilings for almost equal scale factors.

cc/base/math_util.cc

Index: cc/base/math_util.cc
diff --git a/cc/base/math_util.cc b/cc/base/math_util.cc
index 6e5ac0bd45db73b47d318a7d4b3aef0f42af0078..f3ad5ef7a967ad186d7fbbf6987c2ea8341d7560 100644
--- a/cc/base/math_util.cc
+++ b/cc/base/math_util.cc
@@ -120,6 +120,32 @@ static inline void AddVertexToClippedQuad3d(const gfx::Point3F& new_vertex,
   (*num_vertices_in_clipped_quad)++;
 }
 
+float MathUtil::RoundToFixedPrecision(float value, int precision) {
+  DCHECK_GE(precision, 0);
+
+  // The value of std::numeric_limits<float>::digits10 is the number of base-10
+  // digits that can be represented by the type float without change.
+  int max_digits10 = std::numeric_limits<float>::digits10;
+
+  float integral_part;
+  float fractional_part = std::modf(value, &integral_part);
+
+  // Return if |value| can not be represented by float without change.
+  int digits10_in_integral_part =
+      integral_part > 0 ? static_cast<int>(std::log10(integral_part)) + 1 : 1;
+  if (digits10_in_integral_part > max_digits10)
+    return value;
+
+  // Get maximum possible precision.
+  int possible_precision =
+      std::min((max_digits10 - digits10_in_integral_part), precision);
+  DCHECK(possible_precision < max_digits10);
+
+  float factor = std::pow(10, possible_precision);
+  fractional_part = std::round(fractional_part * factor) / factor;
+  return integral_part + fractional_part;
+}
+
 gfx::Rect MathUtil::MapEnclosingClippedRect(const gfx::Transform& transform,
                                             const gfx::Rect& src_rect) {
   if (transform.IsIdentityOrIntegerTranslation()) {